method by which animal and plant substances are prepared for eating by humans. The oil and fat products used for edible purposes can be divided into two distinct classes: liquid oils, such as olive oil, peanut oil, soybean oil, or sunflower oil; and plastic fats, such as lard, shortening, butter, and margarine. The physical nature of the fatty material is unimportant for some uses, but the consistency is a matter of consequence for other products. As a dressing on green salads, for example, a liquid oil is used to provide a coating on the ingredients; a plastic fat such as lard or butter would be unsuitable. Spreads for bread, foods that require a highly developed dough structure, or icings and fillings with a plastic structure require plastic fats rather than liquid oils. For reasons related to both history and climate, there are pronounced geographic patterns of consumption of fats and oils. The ancestors of the present inhabitants of central and northern Europe obtained their...